Errors associated with three methods of assessing respirator fit

Three fit test methods (Bitrex, saccharin, and TSI PortaCount Plus with the N95-Companion) were evaluated for their ability to identify wearers of respirators that do not provide adequate protection during a simulated workplace test. Thirty models of NIOSH-certified N95 half-facepiece respirators (15 filtering-facepiece models and 15 elastomeric models) were tested by a panel of 25 subjects using each of the three fit testing methods. Fit testing results were compared to 5th percentiles of simulated workplace protection factors. Alpha errors (the chance of failing a fit test in error) for all 30 respirators were 71% for the Bitrex method, 68% for the saccharin method, and 40% for the Companion method. Beta errors (the chance of passing a fit test in error) for all 30 respirator models combined were 8% for the Bitrex method, 8% for the saccharin method, and 9% for the Companion method. The three fit test methods had different error rates when assessed with filtering facepieces and when assessed with elastomeric respirators. For example, beta errors for the three fit test methods assessed with the 15 filtering facepiece respirators were < or = 5% but ranged from 14% to 21% when assessed with the 15 elastomeric respirators. To predict what happens in a realistic fit testing program, the data were also used to estimate the alpha and beta errors for a simulated respiratory protection program in which a wearer is given up to three trials with one respirator model to pass a fit test before moving onto another model. A subject passing with any of the three methods was considered to have passed the fit test program. The alpha and beta errors for the fit testing in this simulated respiratory protection program were 29% and 19%, respectively. Thus, it is estimated, under the conditions of the simulation, that roughly one in three respirator wearers receiving the expected reduction in exposure (with a particular model) will fail to pass (with that particular model), and that roughly one in five wearers receiving less reduction in exposure than expected will pass the fit testing program in error.     

Comparison of performance of three different types of respiratory protection devices

Respiratory protection is offered to American workers in a variety of ways to guard against potential inhalation hazards. Two of the most common ways are elastomeric N95 respirators and N95 filtering-facepiece respirators. Some in the health care industry feel that surgical masks provide an acceptable level of protection in certain situations against particular hazards. This study compared the performance of these types of respiratory protection during a simulated workplace test that measured both filter penetration and face-seal leakage. A panel of 25 test subjects with varying face sizes tested 15 models of elastomeric N95 respirators, 15 models of N95 filtering-facepiece respirators, and 6 models of surgical masks. Simulated workplace testing was conducted using a TSI PORTACOUNT Plus model 8020, and consisted of a series of seven exercises. Six simulated workplace tests were performed with redonning of the respirator/mask occurring between each test. The results of these tests produced a simulated workplace protection factor (SWPF). The geometric mean (GM) and the 5th percentile values of the SWPFs were computed by category of respiratory protection using the six overall SWPF values. The level of protection provided by each of the three respiratory protection types was compared. The GM and 5th percentile SWPF values without fit testing were used for the comparison, as surgical masks were not intended to be fit tested. The GM values were 36 for elastomeric N95 respirators, 21 for N95 filtering-facepiece respirators, and 3 for surgical masks. An analysis of variance demonstrated a statistically significant difference between all three. Elastomeric N95 respirators had the highest 5th percentile SWPF of 7. N95 filtering-facepiece respirators and surgical masks had 5th percentile SWPFs of 3 and 1, respectively. A Fisher Exact Test revealed that the 5th percentile SWPFs for all three types of respiratory protection were statistically different. In addition, both qualitative (Bitrex and saccharin) and quantitative (N95-Companion) fit testing were performed on the N95 filtering- and elastomeric-facepiece respirators. It was found that passing a fit test generally improves the protection afforded the wearer. Passing the Bitrex fit test resulted in 5th percentile SWPFs of 11.1 and 7.9 for elastomeric and filtering-facepiece respirators, respectively. After passing the saccharin tests, the elastomeric respirators provided a 5th percentile of 11.7, and the filtering-facepiece respirators provided a 5th percentile of 11.0. The 5th percentiles after passing the N95-Companion were 13.0 for the elastomeric respirators and 20.5 for the filtering-facepiece respirators. The data supports fit testing as an essential element of a complete respiratory protection program.     

Reducing respirator fit test errors: a multi-donning approach

As a continuation of recent studies to assess the accuracy of existing fit test methods, a multi-donning approach to fit testing is presented. As an example of that approach, a multi-donning quantitative fit test for filtering-facepiece respirators is presented and analyzed by comparing its error rates with those of the single-donning approach of current fit test methods. That analysis indicates the multi-donning fit test has the potential to reduce both the alpha error and the beta error to half that of single-donning fit tests. The alpha error is the error of failing a respirator that should pass; the beta error is the error of passing a respirator that should fail. Lowering fit test error rates for filtering-facepiece respirators is important because fit testing is an essential means of helping assure that an individual has selected an adequately fitting respirator. To reduce the alpha and beta error inherent in current fit test methods, the proposed fit test for filtering-facepiece respirators incorporates five donnings of the facepiece, unlike the single donning of existing fit test methods. The analysis presented here indicates that the multiple-donning approach reduces the element of chance in the fit test result and thereby increases the consistency and accuracy of the fit tests. The time to conduct the multi-donning test can approximate the time for current, single-donning tests by shortening the time the respirator is worn after each donning to about 10 sec. And, unlike current fit tests for filtering-facepieces that measure only faceseal leakage, the example multiple-donning fit test considered here is based on a measurement of total leakage (faceseal plus filter). Utilizing total respirator leakage can result in simpler quantitative fit test instrumentation and a fit test that is more relevant to the workplace. Further trials with human subjects are recommended in order to validate the proposed multi-donning approach.     

Simulated workplace protection factors for half-facepiece respiratory protective devices

This study investigates two different methods (random effects model and 5th percentile) for determining the performance of three types of respiratory protective devices (elastomeric N95 respirators, N95 filtering-facepiece respirators, and surgical masks) during a simulated workplace test. This study recalculated the protection level of three types of respiratory protective devices using the random effects model, compared the two methods with each other and the APF of 10 for half-facepiece respirators, and determined the value of each of the fit test protocols in attaining the desired level of simulated workplace protection factor (SWPF). Twenty-five test subjects with varying face sizes tested 15 models of elastomeric N95 respirators, 15 models of N95 filtering-facepiece respirators, and 6 models of surgical masks. Simulated workplace testing was conducted using a TSI PORTACOUNT Plus model 8020 and consisted of a series of seven exercises. Six simulated workplace tests were performed with redonning of the respirator/mask occurring between each test. Each of the six tests produced an SWPF. To determine the level of protection provided by the respiratory protective devices, a 90% lower confidence limit for the simulated workplace protection factor (SWPF(LCL90%)) and the 5th percentile of simulated workplace protection factor were computed. The 5th percentile method values could be up to seven times higher than the SWPF(LCL90%) values. Without fit testing, all half-facepiece N95 respirators had a 5th percentile of 4.6 and an SWPF(LCL90%) value of 2.7. N95 filtering-facepiece respirators as a class had values of 3.3 and 2.0, respectively, whereas N95 elastomeric respirators had values of 7.3 and 4.6, respectively. Surgical masks did not provide any protection, with values of 1.2 and 1.4, respectively. Passing either the Bitrex, saccharin, or Companion fit test resulted in the respirators providing the expected level of protection with 5th percentiles greater than or equal to 10 except when passing the Bitrex test with N95 filtering-facepiece respirators, which resulted in a 5th percentile of only 7.9. No substantial difference was seen between the three fit tests. All of the SWPF(LCL90%) values after passing a fit test were less than 10. The random model method provides a more conservative estimate of the protection provided by a respirator because it takes into account both between- and within-wearer variability.     

The effect of subject characteristics and respirator features on respirator fit

A recent study was conducted to compare five fit test methods for screening out poor-fitting N95 filtering-facepiece respirators. Eighteen models of NIOSH-certified, N95 filtering-facepiece respirators were used to assess the fit test methods by using a simulated workplace protection factor (SWPF) test. The purpose of this companion study was to investigate the effect of subject characteristics (gender and face dimensions) and respirator features on respirator fit. The respirator features studied were design style (folding and cup style) and number of sizes available (one size fits all, two sizes, and three sizes). Thirty-three subjects participated in this study. Each was measured for 12 face dimensions using traditional calipers and tape. From this group, 25 subjects with face size categories 1 to 10 tested each respirator. The SWPF test protocol entailed using the PortaCount Plus to determine a SWPF based on total penetration (face-seal leakage plus filter penetration) while the subject performed six simulated workplace movements. Six tests were conducted for each subject/respirator model combination with redonning between tests. The respirator design style (folding style and cup style) did not have a significant effect on respirator fit in this study. The number of respirator sizes available for a model had significant impact on respirator fit on the panel for cup-style respirators with one and two sizes available. There was no significant difference in the geometric mean fit factor between male and female subjects for 16 of the 18 respirator models. Subsets of one to six face dimensions were found to be significantly correlated with SWPFs (p < 0.05) in 16 of the 33 respirator model/respirator size combinations. Bigonial breadth, face width, face length, and nose protrusion appeared the most in subsets (five or six) of face dimensions and their multiple linear regression coefficients were significantly different from zero (p < 0.05). Lip length was found in only one subset. The use of face length and lip length as the criteria to define the current half-facepiece respirator fit test panel may need to be reconsidered when revising the panel. Based on the findings from this and previous studies, face length and face width are recommended measurements that should be used for defining the panel for half-facepiece respirators.     

Qualitative fitting characteristics of elastomeric half face-piece respirators using Isoamyl acetate agent

To examine the fit testing of elastomeric half face-piece respirators (EHRs), a total of 41 candidates were randomly assigned into seven EHRs equipped with organic vapor (OV) cartridges which were commonly used in the Iranian industrial workplaces. The qualitative fitting into the facial dimensions was assessed using the Allegro Isoamyl Acetate fit test kit. While the studied EHRs showed very low passing fit testing rates, the 3M, AoSafety (Medium), and AoSafety (Large) had the highest passing rates with 22.0%, 14.60%, and 9.76%, respectively. The AoSafety (All sizes) delivered a higher passing fit test rate than the 3M brand (29.30 vs. 22.0%). The one size fits all respirators including the DUO and Climax showed lower proportions of passing fit tests compared with AoSafety three-size system brands (2.40% and 4.90% vs. 29.30%). Low fit test passing rates were determined among different respirators. The respirators with various sizes and styles had more opportunities for different wearers to pass the fit test than single size models. The initial and annual fit testing requirements shall be developed by local government. Also, the manufacturers are required to pay attention to respirator features and subject characteristics during the production to obtain satisfactory protection for the end-users.     

The effects of strapped spectacles on the fit factors of three manufactured brands of full facepiece negative pressure respirators.

A study was conducted to determine the effects of strapped spectacles on the fit factors obtained during quantitative fit testing on three different brands of full facepiece negative pressure respirators. The three brands of respirators were evaluated with and without strapped spectacles worn by the test subjects. A total of 180 quantitative fit testing trials were conducted on ten male test subjects. For each test subject, three quantitative fit testing trials were performed with each brand of respirator with and without the spectacles. The average of the fit testing trials for each subject with each respirator was used for statistical analysis. The results demonstrated that the fit factor values were significantly lower during use of the spectacles (p < 0.05). The estimated percentage of test subjects who failed the American National Standards Institute pass/fail criteria for quantitative fit testing (1000) increased by 15-36% when spectacles were worn.     

Comparison of five methods for fit-testing N95 filtering-facepiece respirators

Five fit-testing methods (Bitrex, ambient aerosol condensation nuclei counter using the TSI PortaCount Plus, saccharin, modified ambient aerosol condensation nuclei counter using the TSI PortaCount Plus with the N95-Companion, and generated aerosol using corn oil) were evaluated for their ability to identify poorly fitting N95 filtering-facepiece respirators. Eighteen models of NIOSH-certified, N95 filtering-facepiece respirators were tested by a panel of 25 subjects using each fit-testing method. The penetration of the corn oil and the ambient aerosols through the filter media of each respirator was measured in order to adjust the corresponding generated and ambient aerosol overall fit factors, reflecting only face-seal leakage. Fit-testing results were compared to 5th percentiles of simulated workplace protection factors. Beta errors (the chance of passing a fit-test in error) ranged from 3 percent to 11 percent. Alpha errors (the chance of failing a fit-test in error) ranged from 51 percent to 84 percent. The ambient aerosol using the TSI PortaCount Plus and the generated aerosol methods identified poorly fitting respirators better than the saccharin, the Companion, and Bitrex methods. These errors rates should be considered when selecting a fit-testing method for fitting N95 filtering-facepieces. When both types of errors were combined as an assignment error, the ambient aerosol method using the TSI PortaCount Plus had the lowest percentage of wearers being assigned a poor-fitting respirator.     

Respiratory protection and the risk of Mycobacterium tuberculosis infection

Tuberculosis (TB) can be transmitted to susceptible healthcare workers via inhalation of droplet nuclei carrying viable Mycobacterium tuberculosis bacilli. Several types of respiratory protective devices are compared with respect to efficacy against droplet nuclei penetration: surgical masks, disposable dust/mist particulate respirators (PRs), elastomeric halfmask respirators with high-efficiency (HEPA) filters, and powered airpurifying respirators (PAPRs) with elastomeric halfmask facepieces and HEPA filters. It is estimated that these devices permit, respectively, 42%, 5.7%, 2%, and 0.39% penetration of droplet nuclei into the facepiece. More limited data for the disposable HEPA filtering-facepiece respirator suggest that it would allow droplet nuclei penetration of 3% or less, similar to the value estimated for the elastomeric halfmask HEPA filter respirator. Because a respirator wearer's cumulative infection risk depends on the extent of droplet nuclei penetration, the cumulative risk will differ, given use of these different respirators. Hypothetical but realistic “low-exposure” and “high-exposure” scenarios are posed that involve, respectively, a 1.6% and a 6.4% annual risk of infection for healthcare workers. For the low-exposure scenario, the 10-year cumulative risks given no respirators versus surgical masks versus disposable dust/mist PRs versus elastomeric halfmask HEPA filter respirators versus HEPA filter PAPRs are, respectively, 15%, 6.7%, 0.94%, 0.33%, and .064%. For the high-exposure scenario, the 10-year cumulative risks for no respirator use versus use of the same four types of respirators are, respectively, 48%, 24%, 3.7%, 1.3%, and 0.26%. The use of disposable HEPA filtering-facepiece respirator should permit cumulative risks close to those estimated for the elastomeric halfmask HEPA filter respirator. It is concluded that when an infectious TB patient undergoes a procedure that generates respiratory aerosols, and when droplet nuclei source control is inadequate, healthcare workers attending the patient may need to wear highly protective respirators, such as HEPA filter PAPRs.     

Fit factors for quarter masks and facial size categories

Respirator fit testing is necessary before entering hazardous working environments to ensure that the respirator, when worn, satisfies a minimum fit and that the wearer knows when the respirator fits properly. In the many countries that do not have fit testing or total inward leakage regulations (including Korea), however, many workers wearing respirators may be potentially exposed to hazardous environments. It is necessary to suggest a useful tool to provide an alternative for fit testing in these countries. This study was conducted to evaluate fitting performance for quarter-mask respirators, and fit factors in facial size categories based on face lengths and lip lengths of the wearers. A total of 778 subjects (408 males, 370 females) were fit tested for three quarter masks: Sejin Co. SK-6 (Ulsan, Korea), Yongsung Co. YS-2010 S (Seoul, Korea), and 3 M Co. Series 7500 Medium (MN, USA) masks with a PortaCount 8020 (TSI Co., USA). A facial dimension survey of the subjects was conducted to develop facial size categories, on the basis of face length and lip length. Geometric mean fit factors (GMFFs) of Series 7500 Medium were found to be the highest of the three respirators. All of the respirators were more suitable for males than females in fitting performance. The Series 7500 Medium fitted a large number of the males tested, since the GMFFs for males were above 100 for every box of facial size categories, and high pass proportion rates were shown at an individual fit factor level of 100. The YS-2010 S provides an adequate fit for males in a limited range of facial dimensions. The Series 7500 Medium is more limited in providing adequate fit for females at specific facial dimensions than for males. For adequate fitting performance, the SK-6 is not preferentially recommended for Korean male and female workers due to low GMFFs and pass proportions. The result of this study indicates that after more accurate studies are performed, facial size categories, on the basis of facial dimensions, could be a useful tool to assist in the selection of adequately fitting respirators for workers in the countries having no fit testing requirements.     

Correlation between respirator fit and respirator fit test panel cells by respirator size

The National Institute for Occupational Safety and Health (NIOSH), recognizing the difficulties inherent in using old military data to define modern industrial respirator fit test panels, recently completed a study to develop an anthropometric database of the measurements of heads and faces of civilian respirator users. Based on the data collected, NIOSH researchers developed two new panels for fit testing half-facepiece and full-facepiece respirators. One of the new panels (NIOSH bivariate panel) uses face length and face width. The other panel is based on principal component analysis (PCA) to identify the linear combination of facial dimensions that best explains facial variations. The objective of this study was to investigate the correlation between respirator fit and the new NIOSH respirator fit test panel cells for various respirator sizes. This study was carried out on 30 subjects that were selected in part using the new NIOSH bivariate panel. Fit tests were conducted on the test subjects using a PORTACOUNT device and three exercises. Each subject was tested with three replications of four models of P-100 half-facepiece respirators in three sizes. This study found that respirator size significantly influenced fit within a given panel cell. Face size categories also matched the respirator sizing reasonably well, in that the small, medium, and large face size categories achieved the highest geometric mean fit factors in the small, medium, and large respirator sizes, respectively. The same pattern holds for fit test passing rate. Therefore, a correlation was found between respirator fit and the new NIOSH bivariate fit test panel cells for various respirator sizes. Face sizes classified by the PCA panel also followed a similar pattern with respirator fit although not quite as consistently. For the LANL panel, however, both small and medium faces achieved best fit in small size respirators, and large faces achieved best fit in medium respirators. These findings support the selection of the facial dimensions for developing the new NIOSH bivariate respirator fit test panel.     

Simulated workplace performance of N95 respirators.

During July 1995 the National Institute for Occupational Safety and Health (NIOSH) began to certify nine new classes of particulate respirators. To determine the level of performance of these respirators, NIOSH researchers conducted a study to (1) measure the simulated workplace performance of 21 N95 respirator models, (2) determine whether fit-testing affected the performance, and (3) investigate the effect of varying fit-test pass/fail criteria on respirator performance. The performance of each respirator model was measured by conducting 100 total penetration tests. The performance of each respirator model was then estimated by determining the 95th percentile of the total penetration through the respirator (i.e., 95% of wearers of that respirator can expect to have a total penetration value below the 95th percentile penetration value). The 95th percentile of total penetrations for each respirator without fit-testing ranged from 6 to 88%. The 95th percentile of total penetrations for all the respirators combined was 33%, which exceeds the amount of total penetration (10%) normally expected of a half-mask respirator. When a surrogate fit test (1% criterion) was applied to the data, the 95th percentile of total penetrations for each respirator decreased to 1 to 16%. The 95th percentile of total penetrations for all the respirators combined was only 4%. Therefore, fit-testing of N95 respirators is necessary to ensure that the user receives the expected level of protection. The study also found that respirator performance was dependent on the value of the pass/fail criterion used in the surrogate fit-test.     

Recommended test methods and pass/fail criteria for a respirator fit capability test of half-mask air-purifying respirators

This study assessed key test parameters and pass/fail criteria options for developing a respirator fit capability (RFC) test for half-mask air-purifying particulate respirators. Using a 25-subject test panel, benchmark RFC data were collected for 101 National Institute for Occupational Safety and Health-certified respirator models. These models were further grouped into 61 one-, two-, or three-size families. Fit testing was done using a PortaCount® Plus with N95-Companion accessory and an Occupational Safety and Health Administration-accepted quantitative fit test protocol. Three repeated tests (donnings) per subject/respirator model combination were performed. The panel passing rate (PPR) (number or percentage of the 25-subject panel achieving acceptable fit) was determined for each model using five different alternative criteria for determining acceptable fit.

When the 101 models are evaluated individually (i.e., not grouped by families), the percentages of models capable of fitting >75% (19/25 subjects) of the panel were 29% and 32% for subjects achieving a fit factor ≥100 for at least one of the first two donnings and at least one of three donnings, respectively. When the models are evaluated grouped into families and using >75% of panel subjects achieving a fit factor ≥100 for at least one of two donnings as the PPR pass/fail criterion, 48% of all models can pass. When >50% (13/25 subjects) of panel subjects was the PPR criterion, the percentage of passing models increased to 70%.

Testing respirators grouped into families and evaluating the first two donnings for each of two respirator sizes provided the best balance between meeting end user expectations and creating a performance bar for manufacturers. Specifying the test criterion for a subject obtaining acceptable fit as achieving a fit factor ≥100 on at least one out of the two donnings is reasonable because a majority of existing respirator families can achieve an PPR of >50% using this criterion. The different test criteria can be considered by standards development organizations when developing standards.     

New respirator fit test panels representing the current U.S. civilian work force

The fit test panels currently used for respirator research, design, and certification are 25-subject panels developed by Los Alamos National Laboratory (LANL) and are based on data from the 1967 and 1968 anthropometric surveys of U.S. Air Force personnel. Military data do not represent the great diversity in face size and shape seen in civilian populations. In addition, the demographics of the U.S. population have changed over the last 30 years. Thus, it is necessary to assess and refine the LANL fit test panels. This paper presents the development of new respirator fit test panels representative of current U.S. civilian workers based on an anthropometric survey of 3,997 respirator users conducted in 2003. One panel was developed using face length and face width (bivariate approach) and weighting subjects to match the age and race distribution of the U.S. population as determined from the 2000 census. Another panel was developed using the first two principal components obtained from a set of 10 facial dimensions (age and race adjusted). These 10 dimensions are associated with respirator fit and leakage and can predict the remaining face dimensions well. Respirators designed to fit these panels are expected to accommodate more than 95% of the current U.S. civilian workers. Both panels are more representative of the U.S. population than the existing LANL panel and may be appropriate for testing both half-masks and full-face piece respirators. Respirator manufacturers, standards development organizations, and government respirator certification bodies need to select the appropriate fit test panel for their particular needs. The bivariate panel is simpler to use than the principal component analysis (PCA) panel and is most similar to the LANL panel currently used. The inclusion of the eight additional facial measurements allows the PCA panel to provide better criteria for excluding extreme face sizes from being used. Because the boundaries of the two new panels are significantly different from the LANL panel, it may be necessary to develop new respirator sizing systems. A new five-category sizing system is proposed.     

Respirator leakage in the pharmaceutical industry of northwest England

Field qualitative fit tests were conducted at 10 separate companies in the Northwest of England to determine the proportion of leaking respirators in a cross-section of pharmaceutical manufacturing industries. The 3 M FT-10 Qualitative Fit Test Apparatus was used to test a total of 211 half-face particulate respirator wearers. Participants wore their own respirators and were asked to don them as they would normally. In all cases, no specific intervention had occurred prior to testing. Results indicated a failure rate of 69% (of the 211 subjects tested, 145 respirators were leaking). Successful results were not associated with the frequency of use (p = 0.71) or years of experience wearing respirators (p = 0.59). Similarly, successful results were not associated with respirator training in the current job (p = 0.38) or training in previous jobs (p = 0.49). Leakage was not consistent across the 10 companies, with two companies exhibiting a 100% failure rate while another company had 26 successful tests in 50 wearers (52% pass rate). Only 35 of the 211 participants performed a negative pressure test. Of these, 80% successfully passed the test, which was significantly greater than the 22% pass rate among those who had not performed the pressure test (p < 0.001).     

The effect of gender and respirator brand on the association of respirator fit with facial dimensions

This study examined the association of facial dimensions with respirator fit considering the effect of gender and respirator brand. Forty-one subjects (20 white females and 21 white males) participated in the study. Each subject was measured for 12 facial dimensions using anthropometric sliding and spreading calipers and a steel measuring tape. Three quantitative fit tests were conducted with the same subject wearing one size of three different brands of half-mask respirators resulting in a total of nine fit tests. Linear mixed model analysis was used to model respirator fit as a function of gender and respirator brand while controlling for facial dimensions. Results indicated that the gender by respirator brand interaction was not statistically significant (p = 0.794), and there was no significant difference in respirator fit between males and females (p = 0.356). There was a significant difference in respirator fit among respirator brands (p < 0.001). Because correlations between facial dimensions and respirator fit differed across gender and respirator brand, six separate linear mixed models were fit to assess which facial dimensions most strongly relate to respirator fit using a "one variable at a step" backward elimination procedure. None of the 12 facial dimensions were significantly associated with respirator fit in all six models. However, bigonial breadth and menton-nasion length were significantly associated with respirator fit in five of the six models, and biectoorbitale breadth, bizygomatic breadth, and lip width were significantly associated with respirator fit in four of the six models. Although this study resulted in significant findings related to the correlation of respirator fit with menton-nasion length and lip width (the dimensions currently used to define the half-mask respirator test panel), other facial dimensions were also shown to be significantly associated with respirator fit. Based on these findings and findings from previous studies, it is suggested that other facial dimensions including bigonial breadth, biectoorbitale breadth, and bizygomatic breadth be considered when designing half-mask respirators, and that face length and lip width alone may not be appropriate in defining test groups whose fit is intended to be representative of worker populations.     

Fitting characteristics of eighteen N95 filtering-facepiece respirators

Four performance measures were used to evaluate the fitting characteristics of 18 models of N95 filtering-facepiece respirators: (1) the 5th percentile simulated workplace protection factor (SWPF) value, (2) the shift average SWPF value, (3) the h-value, and (4) the assignment error. The effect of fit-testing on the level of protection provided by the respirators was also evaluated. The respirators were tested on a panel of 25 subjects with various face sizes. Simulated workplace protection factor values, determined from six total penetration (face-seal leakage plus filter penetration) tests with re-donning between each test, were used to indicate respirator performance. Five fit-tests were used: Bitrex, saccharin, generated aerosol corrected for filter penetration, PortaCount Plus corrected for filter penetration, and the PortaCount Plus with the N95-Companion accessory. Without fit-testing, the 5th percentile SWPF for all models combined was 2.9 with individual model values ranging from 1.3 to 48.0. Passing a fit-test generally resulted in an increase in protection. In addition, the h-value of each respirator was computed. The h-value has been determined to be the population fraction of individuals who will obtain an adequate level of protection (i.e., SWPF >/=10, which is the expected level of protection for half-facepiece respirators) when a respirator is selected and donned (including a user seal check) in accordance with the manufacturer's instructions without fit-testing. The h-value for all models combined was 0.74 (i.e., 74% of all donnings resulted in an adequate level of protection), with individual model h-values ranging from 0.31 to 0.99. Only three models had h-values above 0.95. Higher SWPF values were achieved by excluding SWPF values determined for test subject/respirator combinations that failed a fit-test. The improvement was greatest for respirator models with lower h-values. Using the concepts of shift average and assignment error to measure respirator performance yielded similar results. The highest level of protection was provided by passing a fit-test with a respirator having good fitting characteristics.     

中国成年人呼吸防护用品适合性检验新型头面分栏研究

目的 为满足呼吸防护用品的适配性设计和测试需求,根据目前我国成年人头面测量数据提出2种新的分类(栏)方式:二元分栏和主成分分栏,并分析2种分栏对我国成人头面划分的适用性.方法 以近期我国3000名成年人头面尺寸测量数据为基础建立头面尺寸数据库,根据头面尺寸指标脸长-脸宽的二维分布提出我国成年人头面二元分栏.采用主成分分析对10项稳定的头面尺寸指标(最小额宽、脸宽、鄂宽、脸长、瞳孔间距、头宽、鼻突长、鼻宽、鼻梁宽、鼻长)分析后提出我国成年人头面主成分分栏.通过我国成年人头面数据在不同分栏的分布比例分析两类分栏对成人头面划分的适用性.结果 我国成年人头面二元分栏和主成分分栏分别将脸型分为10个型号和8个型号.总覆盖率分别为96.9%(男性95.4%,女性98.4%)和96.5%(男性95.1%,女性98.1%).各型号覆盖比例较为均匀,二元分栏各型号覆盖率在4.6%～21.7%之间,主成分分栏各型号覆盖率在10.4%～14.6%之间.对比分析国外头面分栏方法,美国洛斯阿拉莫斯实验室(LANL)全面罩分栏只能覆盖我国70.9%的人群,且各型号覆盖极不均匀,其中3个型号的覆盖率之和不足1%;美国国家职业安全卫生研究所(NIOSH)研制的二元分栏和主成分分栏能覆盖我国96.4%和95.9%的人群,但各型号分布不均匀,其二元分栏中5个型号仅覆盖6.3%的人群,主成分分栏中3个型号的覆盖率之和为7.2%.结论 根据我国成人头面数据提出的二元分栏和主成分分栏能代表国人头面尺寸分布,比国外分栏更适用.     

Sensitivity and specificity of the user-seal-check in determining the fit of N95 respirators

N95 respirators are recommended by the World Health Organization (WHO) and the Centers for Disease Control and Prevention (CDC) to prevent the inhalation of droplets which may transmit respiratory pathogens. The reliability of N95 respirators in preventing transmission depends on their fit to the wearer. Quantitative fit testing (QNFT) is the gold standard used to determine this fit objectively. The manufacturers of the respirators also recommend performing a self-reported user-seal-check to detect for leakage. This study aims to investigate the capability of the user-seal-check in determining the fit of N95 respirators by investigating the sensitivity and specificity of the user-seal-check compared with QNFT. A prospective and cross-sectional research design was used. A total of 204 local Chinese undergraduate nursing students were recruited to test two commonly used respirator models (3M 1860S and 3M 1862). The results of the user-seal-check were compared with the results of the gold standard QNFT using the Condensation Nucleus Counter Fit Tester System. The sensitivity and specificity of the user-seal-check results obtained with the respirators were calculated. The results indicated low sensitivity, accuracy and predictive value of the user-seal-check in determining the fit of the N95 respirators. The user-seal-check was not found to be reliable as a substitute for QNFT. The results also suggested that the user-seal-check may be unreliable for detecting gross leakage. We recommend that QNFT is used to determine the fit of N95 respirators.